Newsgroups: comp.robotics
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From: abrown@hpcvcec.cv.hp.com (Allen Brown)
Subject: Re: robot parts: info and question
Message-ID: <1993Feb1.184033.19691@hpcvca.cv.hp.com>
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Organization: Hewlett-Packard Company, Corvallis, Oregon USA
References: <1993Jan31.155957.7778@sbcs.sunysb.edu>
Date: Mon, 1 Feb 1993 18:40:33 GMT
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: I sure wish there was an equivalent volume on the genghis/attila/hannibal
: series.

I agree.

I have a few magazine articles

Discover, March 1991 (Nice picture on the cover) p. 42
  "Invasion Of The Insect Robots" by David H. Freedman
    Includes mention of Attila and a couple of wheeled robots.

The C Users Journal, November 1991 p. 42
  "A Multithreading Library In C For Subsumption Architecture"
  by Richard F. Man

The C Users Journal, November 1992 p. 33
  "A Simple Real-Time Executive" by Charles B. Allison
    Not really about robotics, but potentially useful.

: Is there a reason you didn't consider servos? Price?

They were the first thing I looked at.
  positives:
    Easy to drive electrically
    Easy to mount and already
    Geared to the right range
  negatives: cost (the cheapest I have seen was $20 on sale),
    Not very powerful.  The motor we selected is probably four times
      as powerful as the largest hobby servo I have seen.  And the
      non-hobby servos are astronomical in price.
    No feedback.  There is no way to to determine if the motor has
      stalled before reaching its target position.  This was what
      killed servos as far as I am concerned.
    Cannot run the motor beyond spec.  In a servo the power supply is
      for the control electronics is the same as the motor.  This is
      not good for noise.  It is also not good if you want to run the
      motor at a voltage beyond its rating.  I am considering this to
      allow a greater power to weight ratio.  Of course doing this
      means the robot cannot run continuous duty.

: I have heard of, but been unable to obtain so far, a catalog from
: the "Berg" (sp?) Corporation. They are the "Digikey" of gears, joints,
: etc. I'm not sure about pricing, but I've been told it's relative to
: its competitors in the same way Digikey is to its competitors.

Can anyone else help with this?

:: The main structural components such as body and legs will probably be
:: made of model aircraft plywood and fiberglass.  High strength and low
:: weight are what makes me lean toward them.

: Any references on using fiberglass?

References?  We don't need no skeenkin' references!

Seriously, no.  It just seems like a good idea.  But its hard to
believe that I would be the first to think of it. 

: Is the miniboard too expensive a solution? It does the same thing, and
: has a pretty nice development environment :-).

Our main programmer (and my main partner) has lots of experience with
the Pic.  I think he has a development system.  So that should not be
an issue.

I don't know much about the miniboard.  But I got the impression that
it has no ADCs.  Is that true?

Cost is an issue.  If we can get drive electronics for about $2/motor
(and I think we can) then the total electronics per leg comes to less
than $30.  And that's for a three axis leg.

:: We do not yet have the motor drive electronics.  I am hoping we find a
:: suitable IC.

: How about the SGS-Thompson L293D on the miniboard?

Yes.  I need to get literature on it.

:: We have also not worked out how to measure foot force.  But we know
:: two of the constraints: its gotta be small and cheap.

: There seems to be a deafening silence in c.r about this issue.
: Shane Bouslough       | #include <stddisc.h>

OK.  Ideas:
  Mount piezoelectric plastic on four sides of the leg strut to
    measure bending.
  Use conductive foam under the foot.  Its resistance decreases as it
    gets compressed.
  Place a rubber pad near the bottom of the foot.  Put metal plates on
    top and bottom of the pad.  Measure the capacitance between the
    plates.  This is actually easier than it sounds.  Use the
    capacitor as the timing element in an oscillator and measure the
    output frequency.

Thanks for the feedback.
--
  Allen C. Brown  abrown@cv.hp.com or hplabs!hpcvca!abrown or "Hey you!"
      Not representing my employer.
    The Constitution only guarantees the American people the right to
    pursue happiness.  You have to catch it yourself. --- Benjamin Franklin
